1. Field of the Invention
This invention relates to the presentation and display of mudlog and geophysical log data with hydrocarbon isotopic analysis data associated with oil and gas drilling operations. Specifically, the present invention relates to the display of an interpretive method derived from mud gas isotope logging data to assess hydrocarbon charge, source identification, maturity, reservoir compartmentalization and hydrocarbon communication concomitant with identification of lithological seals, baffles and barriers with conventional oil and gas exploration and production geophysical logs.
2. Description of the Related Art
Laboratory analysis of gas samples obtained during a drilling operation may be employed to determine geochemical information associated with strikes of oil or gas deposits. The laboratory analysis may include the acquisition of compositional and isotopic data of sampled subsurface gases. This data is applied to traditional geochemical plots and templates. The interpretation of this data is used to provide geochemical information on the oil and gas provenance, how thermally mature the hydrocarbons are, whether subsurface post-generation effects were encountered during migration of the gaseous hydrocarbons from the source rock to a reservoir, and any problems or effects the hydrocarbons in the reservoir subsequently experienced.
Existing well sampling techniques use physical gas samples for compositional and isotopic laboratory analyses, obtained via wellheads, separators, down-hole logging tools (e.g., modular dynamic tester/repeat formation tester, etc.), canned cuttings, and/or sampled gases entrained in the mud system during drilling.
As discussed in U.S. Pat. No. 7,124,030, there are several problems and issues not adequately addressed using standard mud gas chromatographic compositional analyses and interpretations. None of the existing techniques effectively detail or correlate geological information such as lithological hydrocarbon seals, baffles and barriers, good communication compartments, or gas diffusion and/or leakage into their interpretation. Compositional data can result in false positives and negatives where changes in operational conditions related to drilling variables such as increased rate of penetration or mud weight increases occur. U.S. Pat. No. 7,124,030 provides a far more advanced method which applies new interpretative techniques involving mud gas chromatographic compositional and isotopic analyses together with detailed drilling, geological and engineering information integration.
Within the improved interpretative techniques disclosed in U.S. Pat. No. 7,124,030 is the newly developed use of hydrocarbon mixing lines to determine or suggest good hydrocarbon communication compartments and zones. Mixing lines are identified on plots where hydrocarbon gas compositional and isotopic data are plotted. The mixing lines are defined by data points falling along a plotted trend line, suggesting a depth section in the well that is in good gas communication, and therefore representative of a compartment. Breaks in any of the mixing lines identify approximate depth locations at which lithological seals, baffles or other barriers to hydrocarbon communication may in fact be present. The depth range of each line may be considered to reflect or suggest an interval of good hydrocarbon communication. Furthermore, a number of seals, baffles and barriers are suggested defining these intervals, supporting the interpretation that these intervals may be likely to show localized hydrocarbon communication zones concomitant with potentially serious compartmentalization issues.
In the oil and gas industry, geophysical well logs have been invaluable in the search for oil and gas because they provide rapid, economical, and detailed information on whether a well is good or bad. A good well is commercially productive which produces enough oil or gas to pay back the cost of drilling and provides for a profit. A bad well is not commercially productive and can result in expensive losses. Oilfield logs are important tools to assist in making this determination. The mud log is used in combination with the electrical logs run on the well to make a decision about whether to complete the hole (i.e., try to produce oil or gas from it) or “plug” the well (i.e., filled with cement and abandoned). In addition, there are many different kinds of electric logs, and only those that provide the best data about the particular hole are likely to be selected and utilized.
Logs are displayed on a wide variety of individual charts/graphs on a long ‘strip’ of paper that are keyed to depths in the well, and may provide information on depth and thickness of strata/formations penetrated by a well, lithologic characteristics and types of formations encountered (such as shale, sandstone, limestone, dolomite), fluid content including presence of oil or gas, porosity, permeability, dip, reservoir pressure etc. The development of new logs, as well as new uses for old logs, is continuously changing.
Currently, there are several types of logs presently used in oilfield drilling operations. For example, there are mudgas logs which show drill time log (e.g., rate of penetration), mud weight, gas logs (e.g., showing total gas & gas chromatographic response of individual gas components together with cuttings logs (e.g., showing lithological description of cuttings such as sand/shale/siltstone/coal/halite etc. Additionally, there exists geophysical well logs which incorporate both electric and radioactive tools among others, and may include depth logs (e.g., MD and TVD, spontaneous potential, gamma ray, resistivity logs (e.g., conventional electrical survey, focused resistivity devices, induction logs, phaser induction logs, etc.), porosity logs (e.g., sonic or acoustic log, etc.), and neutron density logs.
While a well is being drilled, mudlogs are continually recorded. Recent development of ‘measurement-while-drilling’ (MWD) and ‘logging-while-drilling’ (LWD) logs may also be employed during drilling. After a well is drilled, “electric logging tools” may be lowered into the hole on a “wireline” that provides electrical power down to the “tools”, and transmits the tool readings back up. All of these logs are currently utilized to determine rock types at given depths, and to indicate zones of porous rock.
It would be a distinct advantage to incorporate the interpretative techniques disclosed in U.S. Pat. No. 7,124,030 and U.S. patent application Ser. No. 10/952,136 with current mudlog and other geophysical logs. It is an object of the present invention to provide such a system and method.